1. Field of the Invention
This invention relates to biometric data processing and retrieval.
2. Discussion of the Known Art
Biometrics is concerned with measurements of human characteristics, such as the unique pattern of a person's iris or fingerprint, or locations of features on the person's face. Measurements may be recorded at one instant of time, stored in a database, and then compared with new measurements taken and recorded at a later time. An example of a method for computing a biometric measurement is described in U.S. Pat. No. 5,291,560 “Biometric personal identification system based on iris analysis”.
For security applications involving, e.g., access control or identification of individual passengers at airport terminals, biometrics has the advantage that it is difficult or impossible to transfer one individual's biometric measurements to a second individual. On the other hand, tokens such as entry keys can be easily passed between individuals.
The ability of biometric measurements to differentiate one person from another depends on conditions under which measurements are recorded, as well as on the biometric itself. For example, it has been shown that the human iris is highly unique and therefore can be used to identify a single person even within a relatively large database. In the case of an iris biometric, studies have shown that the size of an iris database may have up to 1.2 million records and still allow for a unique match. In the case of a face biometric, the corresponding database must typically be orders of magnitude smaller for optimal performance. Also, the larger the biometric database, the longer any system takes to search through it.
Scalability may not be a problem when a particular biometric deployment has a small number of enrollees, but as biometric technologies become more widespread, there is a need for a process to maintain a database with a large number of enrollees that will enable a unique matching capability and at the same time be convenient for the user.
An approach taken toward resolving the problem of scalability of large biometric databases has been to use a smart card or a swipe card at or near a given biometric device. The concept is that unique biometric information contained in the smart card or swipe card essentially reduces the “database” to a size of just one. While the approach appears attractive from the viewpoint of the biometric matching, there unfortunately is a cost to issuing and maintaining smart/swipe cards, and further, such cards are inconvenient for users and slows down throughput at the biometric device.
Biometrics may be applied in two ways, namely, (i) verification, wherein a separate token is used to locate a single candidate record in a biometric database with which acquired biometric data is compared, and (ii) recognition, wherein a separate token is not used, and user data is acquired on site by a biometric device and then compared with all records in a database. Advantages of the recognition approach are that the user does not need to carry a token, the system operator does not have to manage issuance or loss of the token, and the throughput of users through a biometric system is not slowed by having to follow a process in which a token must be read. Disadvantages of the recognition approach compared to verification are that more processing must be performed in searching through a database, and the volume of data transmitted between the database and a matching processor is much larger and thus may overcome the capacity of a network if several biometric acquisition devices are installed in the network, resulting in an unacceptable response time. Further, even a momentary failure in the network between the matching processor and the database can result in an immediate system failure. Methods have been developed that attempt to improve the efficiency of storage and search through a large database, for example, U.S. Pat. No. 6,070,159 “Method and Apparatus for Expandable Biometric Searching”.
It is typical in access control and other security applications that the rate at which user data is added to a database is much smaller than the rate at which users are scanned and the database is searched. This means that the contents of the database are relatively static, and that the processes in place for managing the database (e.g., adding or deleting records) are essentially manual. Therefore, the database management can be inefficient and difficult to administer in certain applications where the throughput of users is very high compared to other applications, e.g., the identification of passengers at airport terminals or of visitors entering buildings.